$namespace: 'xm' !default;
$block-sel: "-" !default;
$elem-sel: "__" !default;
$mod-sel: "--" !default;

@mixin bfc {
    height: 100%;
    overflow: hidden;
}

@mixin b($block) {
    $B: #{$namespace + $block-sel + $block};
    .#{$B} {
        @content;
    }
}

@mixin e($el) {
   $selector:&;
   @at-root{
    #{$selector + $elem-sel + $el} {
        @content;
      } 
   }
}

@mixin m($m) {
    $selector:&;
    @at-root{
     #{$selector + $mod-sel + $m} {
         @content;
       } 
    }
}